Nitride semiconductor light emitting device and method for manufacturing the same

ABSTRACT

According to one embodiment, in a nitride semiconductor light emitting device, a first clad layer includes an n-type nitride semiconductor. An active layer is formed on the first clad layer, and includes an In-containing nitride semiconductor. A GaN layer is formed on the active layer. A first AlGaN layer is formed on the GaN layer, and has a first Al composition ratio. A p-type second AlGaN layer is formed on the first AlGaN layer, has a second Al composition ratio higher than the first Al composition ratio, and contains a larger amount of Mg than the GaN layer and the first AlGaN layer. A second clad layer is formed on the second AlGaN layer, and includes a p-type nitride semiconductor.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromPCT/JP2009/007049, filed on Dec. 21, 2009, the entire contents of whichare incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a nitride semiconductorlight emitting device and a method for manufacturing the nitridesemiconductor light emitting device.

BACKGROUND

There are conventionally-known nitride semiconductor light emittingdevices in each of which a p-type Mg-doped AlGaN layer as an electronbarrier layer to trap electrons in an active layer is formed on anactive layer including an In-containing nitride semiconductor (see thedescription of Japanese Patent No. 3446660 and Japanese PatentApplication Publication No. 2006-261392, for example).

In the nitride semiconductor light emitting device disclosed in thedescription of Japanese Patent No. 3446660, the p-type AlGaN layerincludes a first p-type AlGaN layer and a second p-type AlGaN layer. Thefirst p-type AlGaN layer is formed by MOCVD (Metal Organic ChemicalVapor Deposition) which uses a N2 gas to inhibit the deterioration ofthe active layer. The second p-type AlGaN layer is formed by MOCVD whichuses a H2 gas to form barrier potential.

In the nitride semiconductor light emitting device, however, the Alcomposition ratio of the first p-type AlGaN layer is almost the same asthat of the second p-type AlGaN layer, and is set at 0.1 or greater. Inaddition, the first p-type AlGaN layer is doped with a large amount ofMg for decreasing the bulk resistance.

As a result, the nitride semiconductor light emitting device entails aproblem that the quality of the active layer is deteriorated due toexcessive diffusion of Mg into the active layer in the process offorming the second p-type AlGaN layer.

The nitride semiconductor light emitting device disclosed in JapanesePatent Application Publication No. 2006-261392 has an intermediate layerbetween the active layer and the p-type AlGaN layer for the purpose ofinhibiting excessive diffusion of Mg into the active layer. Theintermediate layer includes an undoped GaN layer, an undoped AlGaN layerand the like.

In the case of the nitride semiconductor light emitting device, however,the temperature of the substrate is raised while the intermediate layeris being grown on the active layer. As a result, the nitridesemiconductor light emitting device has a problem that the active layerthermally deteriorates during the temperature rise, and accordinglyentails the quality degradation.

In short, the nitride semiconductor light emitting devices have problemssuch as the decrease in the light-emission efficiency and theincapability of producing sufficient light output.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the nitride semiconductor lightemitting device according to an embodiment;

FIG. 2 is a diagram showing the depth profile of Mg in the nitridesemiconductor light emitting device;

FIG. 3 is a diagram showing the light emission efficiency of the nitridesemiconductor light emitting device in comparison with a light emissionefficiency of a first comparative example;

FIG. 4 is a cross-sectional view showing the first comparative example;

FIG. 5 is a diagram showing the light emission efficiency of the nitridesemiconductor light emitting device in comparison with a light emissionefficiency of a second comparative example;

FIG. 6 is a cross-sectional view showing the second comparative example;

FIG. 7 is a diagram showing the light emission efficiency of the nitridesemiconductor light emitting device in comparison with a light emissionefficiency of a third comparative example;

FIGS. 8 to 11 are cross-sectional views showing the steps ofmanufacturing the nitride semiconductor light emitting device in thesequential order.

DETAILED DESCRIPTION

According to one embodiment, in a nitride semiconductor light emittingdevice, a first clad layer includes an n-type nitride semiconductor. Anactive layer is formed on the first clad layer, and includes anIn-containing nitride semiconductor. A GaN layer is formed on the activelayer. A first AlGaN layer is formed on the GaN layer, and has a firstAl composition ratio. A p-type second AlGaN layer is formed on the firstAlGaN layer, has a second Al composition ratio higher than the first Alcomposition ratio, and contains a larger amount of Mg than the GaN layerand the first AlGaN layer. A second clad layer is formed on the secondAlGaN layer, and includes a p-type nitride semiconductor.

According to another embodiment, in a method for manufacturing a nitridelight emitting device, an active layer including an In-containingnitride semiconductor is formed on a first clad layer including ann-type nitride semiconductor. A GaN layer and a first AlGaN layer havinga first Al composition ratio are formed on the active layer in order bymetal organic chemical vapor deposition at a first growth temperature ina nitrogen gas atmosphere without doping with Mg. A second AlGaN layeris formed on the first AlGaN layer by metal organic chemical vapordeposition at a second growth temperature, in an atmosphere mainlycontaining a hydrogen gas with doping with Mg. The second AlGaN layerhas a second Al composition ratio larger than the first Al compositionratio. The second growth temperature is higher than the first growthtemperature. A second clad layer including a p-type nitridesemiconductor is formed on the second AlGaN layer.

Hereinafter, embodiments will be described with reference to thedrawings. In the drawings, same reference characters denote the same orsimilar portions.

Embodiment

A nitride semiconductor light emitting device of an embodiment will bedescribed with reference to FIG. 1. FIG. 1 is a cross-sectional viewshowing the nitride semiconductor light emitting device.

In a nitride semiconductor light emitting device 10 of the embodiment,as shown in FIG. 1, a gallium nitride layer 12 (hereinafter referred toas a “GaN layer” 12) with a thickness of approximately 3 μm is formed ona substrate 11 transparent to light-emission wavelengths, for example,on a sapphire substrate with a buffer layer (not illustrated) interposedin between.

An n-type gallium nitride clad layer 13 (hereinafter referred to as an“n-type GaN clad layer” 13 or a “first clad layer” 13) with a thicknessof approximately 2 μm, which is doped with silicon (Si), is formed onthe GaN layer 12.

An active layer 14 including an In-containing nitride semiconductor isformed on the n-type GaN clad layer 13. The active layer 14 is amulti-quantum well (MQW) active layer including 5-nanometer-thickgallium nitride barrier layers 15 (each hereinafter referred to as a“GaN barrier layer” 15) and 2.5-nanometer-thick indium gallium nitridewell layers 16 (each hereinafter referred to as an “InGaN well layer”16), which are alternately stacked one on another, with the InGaN welllayer 16 placed atop, for example. The active layer 14 will behereinafter referred to as an “MQW active layer” 14.

A composition ratio x of In to InGaN in each InGaN well layer 16 (theIn_(x)Ga_(1-x)N layer, 0<x<1) is set at approximately 0.1 for thepurpose of making a peak light-emission wavelength equal toapproximately 450 nm, for example.

A gallium nitride layer 17 (hereinafter referred to as a “GaN layer” 17)is formed on the MQW active layer 14. A first AlGaN layer 18, in which acomposition ratio x1 of Al to AlGaN (hereinafter referred to as a “firstAl composition ratio”) is small, is formed on the GaN layer 17. Thecomposition of the first AlGaN layer is expressed with Al_(x1)Ga_(1-x1)N(0<x<1).

The GaN layer 17 and the first AlGaN layer 18 are formed without doping,as described later. Accordingly, the GaN layer 17 and the first AlGaNlayer 18 function as cap layers to inhibit the thermal deterioration ofthe MQW active layer 14 and the diffusion of Mg into the MQW activelayer 14 during a temperature rising step.

Hereinafter, the GaN layer 17 will be referred to as a GaN cap layer 17,and the first AlGaN layer 18 will be referred to as an AlGaN cap layer18.

With this taken into consideration, the AlGaN cap layer 18 needs acombination of the Al composition ratio x1 and the thickness whichsatisfies the following two requirements: a requirement that the AlGaNcap layer 18 should effectively inhibit the thermal deterioration of theMQW active layer 14 in order that the light emission efficiency shouldnot be impaired, and a requirement that the AlGaN cap layer 18 should beable to obtain a lower bulk resistance in order that the operationvoltage should not be disturbed.

The GaN cap layer 17 needs the thickness which satisfies the followingtwo requirements: a requirement that the GaN cap layer 17 should absorbMg which diffuses into the GaN cap layer 17, and a requirement that thefunction of a p-type AlGaN layer serving as an electron barrier layer totrap electrons in the MQW active layer 14, which will be describedlater, should not be impaired.

In this respect, the thickness of the GaN cap layer 17 is set atapproximately 5 nm, for example. It is desirable that the Al compositionratio x1 of the AlGaN cap layer 18 should be greater than zero but notgreater than 0.01. The Al composition ratio x1 of the AlGaN cap layer 18is set at 0.003, for example. The thickness of the AlGaN cap layer 18 isset at 1 nm, for example.

A p-type AlGaN electron barrier layer 19 (hereinafter referred to as a“second AlGaN layer” 19 from time to time) to trap electrons in the MQWactive layer 14 is formed on the AlGaN cap layer 18. The second AlGaNlayer 19 is doped with Mg in a high concentration. The composition ofthe second AlGaN layer is expressed with Al_(x2)Ga_(1-x2)N (0<x2<1 andx1<x2).

A composition ratio x2 of Al to Al_(x2)Ga_(1-x2)N in the p-type AlGaNelectron barrier layer 19 (hereinafter referred to as a “second Alcomposition ratio) is larger than the Al composition ratio x1, and isset at 0.1 to 0.2, for example.

The concentration of Mg in the p-type AlGaN electron barrier layer 19 isset at approximately 1E19 to 1E20 cm⁻³, for example. The thickness ofthe p-type AlGaN electron barrier layer 19 is approximately 10 nm, forexample.

A p-type gallium nitride clad layer 20 (hereinafter referred to as a“p-type GaN clad layer” 20 or a “second clad layer” 20) is formed on thep-type AlGaN electron barrier layer 19. The p-type GaN clad layer 20 isapproximately 100 nm in thickness, and is doped with Mg in a highconcentration, for example. The concentration of Mg in the p-type GaNclad layer 20 is set at approximately 1E19 to 1E20 cm⁻³, for example.

A p-type gallium nitride contact layer 21 (hereinafter referred to as a“p-type GaN contact layer” 21) is formed on the p-type GaN clad layer20. The p-type GaN contact layer 21 is approximately 10 nm in thickness,and is doped with Mg in a concentration which is higher than theconcentration of Mg in the p-type GaN clad layer 20, for example. Theconcentration of Mg in the p-type GaN contact layer 21 is set atapproximately 1E20 to 1E21 cm⁻³, for example.

A p-side electrode 22 made of Ni/Au is formed on the p-type GaN contactlayer 21. In addition, one lateral portion of the nitride semiconductorlight emitting device 10 is dug in from the p-type GaN contact layer 21to a portion of the n-type GaN clad layer 13, and an n-side electrode 23made of Ti/Pt/Au is formed on an exposed portion of the n-type GaN cladlayer 13. The n-type GaN clad layer 13 functions as an n-type GaNcontact layer at the same time.

Light is emitted from the MQW active layer 14 when an electric currentis caused to pass between the p-side electrode 22 and the n-sideelectrode 23 with the p-side electrode 22 and the n-side electrode 23connected to the respective positive and negative electrodes of a powersupply.

In this respect, the functions respectively of the n-type GaN clad layer13, the MQW active layer 14, the p-type GaN clad layer 20 and the p-typeGaN contact layer 21 are well known. For this reason, descriptions forthese layers are omitted.

The thus-structured nitride semiconductor light emitting device isconfigured in a way that, during the formation of the p-type AlGaNelectron barrier layer 19 to the p-type GaN contact layer 21 which aredoped with Mg in the high concentration, the effect of inhibiting thethermal deterioration of the MQW active layer 14 and the effect ofpreventing the diffusion of Mg into the MQW active layer 14 are enhancedby optimizing the two-layered structure including: the GaN cap layer 17for which the thick film having a better crystallinity can be formedeven at a relatively low growth temperature; and the AlGaN cap layer 18which is capable of effectively inhibiting the thermal deterioration ofthe MQW active layer 14 because of the chemical stability exhibited at arelative high melting point.

For the purpose of checking this, an examination was made on the depthprofile of Mg in the nitride semiconductor light emitting device 10. Theresult of the examination will be explained with reference to FIG. 2.

The other examination was further made on the influence of the GaN caplayer 17, the AlGaN cap layer 18 and the Al composition ratio x1 on thelight emission efficiency. The result of the examination will beexplained with reference to FIGS. 3 to 7.

FIG. 2 is a diagram showing the depth profile of Mg in the nitridesemiconductor light emitting device 10. The depth profile of Mg wasobtained by use of the SIMS (Secondary Ion Mass Spectrometry).

In addition to the depth profile of Mg, FIG. 2 shows: the depth profileof hydrogen (H), which exhibited the same behavior as did Mg because Hwas taken in through the bonding of H with Mg during the film formation;and the secondary ionic strengths respectively of Al and In which wereused as markers to identify the layers.

A thick continuous line indicates the depth profile of Mg, and a thincontinuous line indicates the depth profile of H. In addition, a dashedline indicates the secondary ionic strength of Al, and a chain lineindicates the secondary ionic strength of In.

It was learned from the secondary ionic strength respectively of Al andIn as well as the depth profiles that, as shown in FIG. 2, the depth ofthe interface between the MQW active layer 14 and the undoped GaN caplayer 17 was approximately 100 nm from the surface (the design value was126 nm, for example).

No significant diffusion of Mg into the MQW active layer 14 wasobserved, because the gradients (approximately 7 nm/decade) of the risesof the secondary ionic strengths of Al and In were almost the same asthe gradient of the fall of the concentration of Mg which was not higherthan the background level (approximately 5E18 cm⁻³) of the concentrationof H. This tells that Mg in the MQW active layer 14 was well below thedetection limit.

In addition, the concentration of Mg in each of the undoped GaN caplayer 17 and the undoped AlGaN cap layer 18 was estimated at 1E18 cm⁻³or less.

As a result, it was confirmed that the diffusion of Mg into the MQWactive layer 14 was effectively inhibited by the two-layered structureincluding: the undoped thick GaN cap layer 17; and the undoped thinAlGaN cap layer 18 in which the Al composition ratio x1 was low.

FIG. 3 is a diagram showing a dependency of the light emissionefficiency of the nitride semiconductor light emitting device 10 on anelectric current in comparison with a dependency of the light emissionefficiency of a first comparative example on an electric current. FIG. 4is a cross-sectional view of the first comparative example.

The dependency of the light emission efficiency of each nitridesemiconductor light emitting device was obtained by measuring theintensity of light emitted from the nitride semiconductor light emittingdevice by use of an integrating sphere while changing the electriccurrent to be supplied to the nitride semiconductor light emittingdevice; and dividing the intensity of the light by the supplied electriccurrent.

In general, the dependency of the light emission efficiency of anynitride semiconductor light emitting device tends to decrease as theelectric current increases, except for a low range of the electriccurrent at and immediately after the time of the rise. This stems fromsomething such as: the decrease in the efficiency of the carrierinjection which occurs because the probability of injected carriersoverflowing from the MQW active layer 14 becomes larger as the electriccurrent increases; and the decrease in the internal quantum efficiencyof the MQW active layer which occurs due to the heat generation.

In this respect, the first comparative example was a nitridesemiconductor light emitting device 40 which, as shown in FIG. 4, didnot include the undoped thick GaN cap layer 17. To begin with, the firstcomparative example is explained. As shown in FIG. 3, the nitridesemiconductor light emitting device 40 of the first comparative exampleexhibited almost the same light emission efficiency as did the nitridesemiconductor light emitting device 10 of the embodiment, while theelectric current was 5 mA or less. However, the light emissionefficiency of the nitride semiconductor light emitting device 40 of thefirst comparative example decreased rapidly as the electric currentincreased.

On the other hand, the light emission efficiency of the nitridesemiconductor light emitting device 10 of the embodiment decreasedslowly as the electric current increased. In addition, higher lightemission efficiency was obtained from the nitride semiconductor lightemitting device 10 of the embodiment than from the nitride semiconductorlight emitting device 40 of the first comparative example.

The rate of the increase in the light emission efficiency wasapproximately 9% when the electric current was 20 mA, and approximately17% when the electric current was 50 mA. The rate of the increase tendedto increase as the electric current increased.

This suggests that particularly the undoped thick GaN cap layer 17inhibited the diffusion of Mg into the MQW active layer 14.

FIG. 5 is a diagram showing the dependency of the light emissionefficiency of the nitride semiconductor light emitting device 10 on theelectric current in comparison with the dependency of the light emissionefficiency of a second comparative example on the electric current. FIG.6 is a cross-sectional view of the second comparative example.

In this respect, the second comparative example was a nitridesemiconductor light emitting device 60 which, as shown in FIG. 6, didnot include the undoped thin AlGaN cap layer 18 in which the Alcomposition ratio x1 was low. To begin with, the second comparativeexample will be explained.

As shown in FIG. 5, the nitride semiconductor light emitting device 60of the second comparative example exhibited almost the same lightemission efficiency as did the nitride semiconductor light emittingdevice 10 of the embodiment, while the electric current was 10 mA orless. However, the light emission efficiency of the nitridesemiconductor light emitting device 60 of the second comparative exampledecreased rapidly as the electric current increased.

On the other hand, the light emission efficiency of the nitridesemiconductor light emitting device 10 of the embodiment decreasedslowly as the electric current increased. In addition, higher lightemission efficiency was obtained from the nitride semiconductor lightemitting device 10 of the embodiment than from the nitride semiconductorlight emitting device 60 of the second comparative example.

The rate of the increase in the light emission efficiency wasapproximately 3% when the electric current was 20 mA, and approximately6% when the electric current was 50 mA. The rate of the increase tendedto increase as the electric current increased.

This suggests that even the thin AlGaN cap layer 18 in which the Alcomposition ratio x1 was low efficiently inhibited the thermaldeterioration of the MQW active layer 14.

FIG. 7 is a diagram showing the dependency of the light emissionefficiency of the nitride semiconductor light emitting device 10 on theelectric current in comparison with the dependency of the light emissionefficiency of a third comparative example on the electric current. Inthis respect, the third comparative example was a nitride semiconductorlight emitting device including an AlGaN cap layer with a higher Alcomposition ratio x1.

FIG. 7 is the diagram showing the dependency of the light emissionefficiency of each of: the nitride semiconductor light emitting device10 of the embodiment where the Al composition ratio x1 in the AlGaN caplayer 18 was 0.003; and the nitride semiconductor light emitting deviceof the third comparative example where the Al composition ratio x1 inthe AlGaN cap layer was 0.05.

As shown in FIG. 7, the dependency of the light emission efficiency onthe electric current was almost the same between the nitridesemiconductor light emitting device 10 of the embodiment and the nitridesemiconductor light emitting device of the third comparative example.However, higher light emission efficiency was obtained from the nitridesemiconductor light emitting device 10 of the embodiment than from thenitride semiconductor light emitting device of the third comparativeexample in the full range of the electric current.

The rate of the increase in the light emission efficiency wasapproximately 3% when the electric current was 20 mA, and approximately2.2% when the electric current was 50 mA. The rate of the increase inthe light emission efficiency per unit increase in the electric currenttended to be almost constant.

This suggests that because the crystallinity of the AlGaN layerincreased as the Al composition ratio became lower, the effect ofinhibiting the diffusion of Mg into the MQW active layer 14 was betterin the AlGaN cap layer 18 than in the AlGaN cap layer of the thirdcomparative example.

From this, it was confirmed that the optimizing of the two-layeredstructure including the GaN cap layer 17 and the AlGaN cap layer 18created the synergism between the effect of inhibiting the thermaldeterioration of the MQW active layer 14 and the effect of preventingthe diffusion of Mg into the MQW active layer 14.

Next, a method for manufacturing the nitride semiconductor lightemitting device 10 will be explained with reference to FIGS. 8 to 11.FIGS. 8 to 11 are cross-sectional views showing the manufacturing stepsfor the nitride semiconductor light emitting device 10 in the sequentialorder.

First of all, as a preliminary treatment, a substrate 11, for example, aC-plane sapphire substrate is subjected to organic cleaning and acidcleaning, for example. Thereafter, the resultant substrate 11 iscontained in a reaction chamber of the MOCVD system. Subsequently, thetemperature Ts of the substrate 11 is raised to T0, for example, 1100°C. by high-frequency heating in a normal-pressure atmosphere of a mixedgas of a nitrogen (N₂) gas and a hydrogen (H₂) gas. Thereby, the surfaceof the substrate 11 is etched in gas phase, and a natural oxide filmformed on the surface of the substrate 11 is removed.

Afterward, as shown in FIG. 8, the undoped GaN layer 12 with a thicknessof 3 μm is formed by using the mixed gas of the N₂ gas and the H₂ gas asa carrier gas while supplying an ammonium (NH₃) gas and trimethylgallium (TMG), for example, as process gases.

Subsequently, the n-type GaN clad layer 13 with a thickness of 2 μm isformed while supplying a silane (SiH₄) gas, for example, as the n-typedopant.

Thereafter, the temperature Ts of the substrate 11 is decreased to andkept at T1, for example, 800° C. which is lower than T0, whilecontinuing supplying the NH₃ gas with the supply of TMG and the SiH₄ gasstopped.

Afterward, as shown in FIG. 9, the GaN barrier layer 15 with a thicknessof 5 nm is formed by using the N₂ gas as the carrier gas while supplyingthe NH₃ gas and TMG, for example, as the process gases. After that, theInGaN well layer 16 with a thickness of 2.5 nm, in which the Incomposition ratio is 0.1, is formed by supplying trimethyl indium (TMI)as another process gas.

Subsequently, the forming of the GaN barrier layer 15 and the forming ofthe InGaN well layer 16 are alternately repeated 7 times, for example,while intermittently supplying TMI. Thereby, the MQW active layer 14 isobtained.

Thereafter, as shown in FIG. 10, the undoped GaN cap layer 17 with athickness of 5 nm is formed while continuing supplying TMG and the NH₃gas with the supply of TMI stopped.

Afterward, the undoped AlGaN cap layer 18 with a thickness of 1 nm, inwhich the Al composition ratio is 0.003, is formed while supplyingtrimethyl aluminum (TMA) with the supply of TMG continuing.

After that, the temperature Ts of the substrate 11 is raised to and keptat T2, for example, 1030° C. which is higher than Ti, in the N₂ gasatmosphere while continuing supplying the NH₃ gas with the supply of TMAstopped.

Subsequently, as shown in FIG. 11, the p-type AlGaN electron barrierlayer 19 with a thickness of 10 nm, in which the concentration of Mg is1E19 to 20 cm⁻³, is formed by using the mixed gas of the N₂ gas and theH₂ gas as the carrier gas while supplying: the NH₃ gas, TMG and TMA asthe process gases; and bis(cyclopentadienyl) magnesium (Cp2Mg) as thep-type dopant.

Thereafter, the p-type GaN clad layer 20 with a thickness ofapproximately 100 nm, in which the concentration of Mg is 1E20 cm⁻³, isformed while continuing supplying TMG and Cp2Mg with the supply of TMAstopped.

Thereafter, the p-type GaN contact layer 21 with a thickness ofapproximately 10 nm, in which the concentration of Mg is 1E21 cm⁻³, isformed while supplying an increased amount of Cp2Mg.

Afterward, the temperature Ts of the substrate 11 is lowered naturallywith the supply of only the carrier gas continued while continuingsupplying the NH₃ gas with the supply of TMG stopped. The supplying ofthe NH₃ gas is continued until the temperature Ts of the substrate 11reaches 500° C.

After that, the resultant substrate 11 is taken out of the MOCVD system.Subsequently, a portion of the resultant substrate 11 is removed by RIE(reactive ion etching) until the removed portion reaches the n-type GaNclad layer 13. Thereafter, the n-side electrode 23 made of Ti/Pt/Au isformed on the exposed portion of the n-type GaN clad layer 13.

Furthermore, the p-side electrode 22 made of Ni/Au is formed on thep-type GaN contact layer 21. The nitride semiconductor light emittingdevice 10 shown in FIG. 1 is obtained through these steps.

The measurement of the I-V (current-voltage) characteristic of thenitride semiconductor light emitting device 10 shows that the operationvoltage is 3.1 to 3.5V when the electric current is 20 mA. On thisoccasion, approximately 15 mW is obtained as the light output. The peakwavelength of the light emission is approximately 450 nm.

In the embodiment, as described above, the undoped thick GaN cap layer17 and the undoped thin AlGaN cap layer 18, in which the Al compositionratio x1 is low, are formed at the temperature which is equal to thetemperature T1 for forming the MQW active layer 14.

As a result, the thermal deterioration of the MQW active layer 14 isprevented while the temperature is raised from the temperature T1 to thetemperature T2. In addition, the diffusion of Mg into the MQW activelayer 14 can be prevented while the p-type AlGaN electron barrier layer19 and the p-type GaN contact layer 21 are formed at the temperature T2.

Thereby, the quality of the MQW active layer 14 is maintained. Thismakes it possible to obtain: the nitride semiconductor light emittingdevice capable of offering the sufficient light output; and the methodfor manufacturing the same.

The film thickness of the GaN cap layer 17 as well as the Al compositionratio x1 and the film thickness of the AlGaN cap layer 18, which arementioned in the foregoing descriptions of the embodiment, are shown asthe examples. It is more desirable that the film thickness of the GaNcap layer 17 as well as the Al composition ratio x1 and the filmthickness of the AlGaN cap layer 18 should be optimized depending on thestructure of the nitride semiconductor light emitting device, themanufacturing conditions for the nitride semiconductor light emittingdevice, and the like within the scope not departing from the gist whichhas been described above.

The foregoing descriptions have been provided for the case where theC-plane sapphire substrate is used as the substrate 11. However, anothersubstrate, for example, a GaN substrate, a SiC substrate, a ZnOsubstrate or something similar may be used as the substrate 11.

Furthermore, the plane orientation of the substrate 11 is not limited tothe C-plane. Another plane, for example, a nonpolar plane may be used.

The foregoing descriptions have been provided for the case where MOCVDis used as the film-forming technique for a nitride semiconductor layer.However, another film-forming technique, for example, hydride vaporphase epitaxy (HVPE), molecular beam epitaxy (MBE), or something similarmay be used.

The foregoing descriptions have been provided for the case where TMG,TMA, TMI, NH₃ are used as the process gases. However, another processgas, for example, triethyl gallium (TEG) may be used.

1.-9. (canceled)
 10. A method for manufacturing a nitride semiconductorlight emitting device, comprising: forming an active layer including anIn-containing nitride semiconductor on a first layer including an n-typenitride semiconductor; forming a GaN layer and a first AlGaN layerhaving a first Al composition ratio on the active layer in order bymetal organic chemical vapor deposition at a first growth temperature ina nitrogen gas atmosphere without doping with Mg; forming a second AlGaNlayer on the first AlGaN layer by metal organic chemical vapordeposition at a second growth temperature, in an atmosphere mainlycontaining a hydrogen gas with doping with Mg, the second AlGaN layerhaving a second Al composition ratio larger than the first Alcomposition ratio, and the second growth temperature being higher thanthe first growth temperature; and forming a second layer including ap-type nitride semiconductor on the second AlGaN layer.
 11. The methodfor manufacturing the nitride semiconductor light emitting deviceaccording to claim 10, wherein the first Al composition ratio is greaterthan 0 and not greater than 0.01.
 12. The method for manufacturing thenitride semiconductor light emitting device according to claim 10,wherein a concentration of Mg in each of the GaN layer and the firstAlGaN layer is not greater than 1E18 cm⁻³.
 13. The method formanufacturing the nitride semiconductor light emitting device accordingto claim 10, wherein the first AlGaN layer has a smaller thickness thanthe GaN layer.
 14. The method for manufacturing the nitridesemiconductor light emitting device according to claim 10, wherein aconcentration of Mg in the GaN layer is not greater than 1E18 cm⁻³. 15.The method for manufacturing the nitride semiconductor light emittingdevice according to claim 10, wherein a concentration of Mg in the firstAlGaN layer is not greater than 1E18 cm⁻³.
 16. The method formanufacturing the nitride semiconductor light emitting device accordingto claim 10, wherein a concentration of Mg in the GaN layer is notgreater than 1E18 cm⁻³, the first AlGaN layer is formed on the GaNlayer, the first Al composition ratio is greater than 0 and not greaterthan 0.01, a concentration of Mg in the first AlGaN layer is not greaterthan 1E18 cm⁻³ and the first AlGaN layer has a smaller thickness thanthe GaN layer.